1. Field of the Invention
This invention broadly relates to appliances that are used during the course of orthodontic treatment. More particularly, the invention relates to orthodontic appliances such as brackets that are directly bonded to the surfaces of teeth, methods for bonding orthodontic appliances to teeth and methods for making orthodontic appliances.
2. Description of the Related Art
Orthodontic treatment involves the movement of malpositioned teeth to orthodontically correct locations. Orthodontic treatment is often undertaken to improve the patient""s facial appearance. In addition, orthodontic treatment when completed can provide improved occlusion and help avoid undue wear on the teeth enamel that might otherwise create additional problems in the future.
One type of common orthodontic treatment includes the use of a set of tiny, slotted appliances known as brackets. Each of the brackets is mounted on an outer surface of the patient""s tooth, and an archwire is placed in the slot of each bracket. The archwire forms a track to guide movement of the brackets such that the associated teeth are brought into positions of correct alignment. Ends of the archwire are often received in small molar appliances, also called buccal tubes, that are mounted on molar teeth of each dental arch.
Many commercially available orthodontic appliances are adapted to be directly bonded to the outer surface of the patient""s teeth by an orthodontic bonding adhesive. Some types of orthodontic adhesives are initially supplied as two separate components, such as CONCISE brand adhesive from 3M Unitek. As the components are mixed together, the components react with each other to form an adhesive that ultimately hardens and provides sufficient strength to bond the appliance to the tooth.
Two-component orthodontic adhesives have a certain xe2x80x9cworking timexe2x80x9d. During the working time, the practitioner transfers the mixed adhesive to the base of the appliance, places the appliance on the tooth and shifts the appliance as may be needed to a desired position on the tooth, all before the adhesive begins to harden. However, if the working time is too short or if the practitioner is interrupted during the procedure, the practitioner may not have sufficient time to precisely place the appliance in its intended position on the tooth surface. On the other hand, if the working time is too long, there is a risk that the appliance will shift from its intended position before the adhesive hardens. Unintentional appliance movement may occur, for example, if the appliance is bumped or jarred, or if the adhesive has a viscosity that enables the appliance to drift along the surface of the tooth. Unfortunately, appliances that are mispositioned once bonded to the teeth represent a significant nuisance to the practitioner as well as to the patient, especially in instances when the appliance must be removed from the tooth and rebonded at the correct location.
For the reasons set out above, many orthodontic practitioners prefer to use a photopolymerizable adhesive that begins to harden once a source of light is directed toward the adhesive. Photopolymerizable adhesives, also known as light-curable adhesives, are used by many orthodontic practitioners because the length of the working time can be chosen as needed. For example, an appliance with a light-curable adhesive can be carefully placed on the patient""s tooth and shifted as desired until such time as the practitioner is satisfied with the position of the appliance. At that time, a source of light is directed toward the adhesive in order to harden the adhesive and quickly fix the appliance to the tooth.
Over the years, many attempts have been made to increase the strength of the bond between orthodontic appliances and the associated teeth. Some brackets, for example, have an outer base surface that is roughened, scribed or dimpled, while other brackets have a base surface that includes one or more layers of irregularly shaped fragments or spherical particles. Such base surfaces present an increased surface area that is available for contact with the adhesive, in order to improve the strength of the bond between the appliance and the tooth.
Additionally, certain orthodontic appliances have bases that present undercut regions to receive the adhesive. Once the adhesive has hardened, the adhesive in the undercut regions forms a mechanical interlock with the appliance. As an example, the bases of some appliances have a fine mesh metal xe2x80x9cscreenxe2x80x9d or pad that becomes embedded in the adhesive and provides a mechanical interlock with the adhesive once the adhesive has hardened. Other appliances, such as that shown in U.S. Design Pat. No. 290,040, have a series of undercut grooves that provide a mechanical interlock with the hardened adhesive. U.S. Pat. Nos. 4,094,068 and 5,435,720 describe appliances having bases with peripheral holes or notches that enable the adhesive to flow through and produce an enlarged head that serves to improve retention of the appliance on the tooth. Orthodontic appliances may also have irregularly-shaped fragments or spherical particles that present undercut regions.
Orthodontic appliances are available in a variety of materials, including metallic materials (such as stainless steel and titanium), plastics (such as filled and/or reinforced polycarbonate) and ceramics (such as monocrystalline and polycrystalline alumina). Some orthodontic practitioners and patients prefer appliances that are made of transparent or translucent materials such as certain plastics and ceramics, because those appliances can blend in with the color of the patient""s teeth and as a result are less noticeable in the oral cavity. Some orthodontic appliances, such as those described in applicants U.S. Pat. No. 4,954,080, are made of a polycrystalline alumina material that has sufficient translucency to enable the color of the tooth to be visible through the appliance in order to provide an enhanced aesthetic appearance.
When a photopolymerizable orthodontic adhesive is used in combination with an appliance that is made of a translucent or transparent material, light passing through the appliance can normally reach the underlying adhesive. As a result, the adhesive is usually hardened to a substantial extent under most, if not all, portions of the appliance base. The extent of hardening of the adhesive helps ensure that the appliance does not spontaneously debond from the patient""s tooth during the course of orthodontic treatment.
Many practitioners, however, prefer to use orthodontic appliances that are made of materials other than light-transmissive plastic and ceramic materials. For example, a substantial number of orthodontists prefer to use appliances made of stainless steel. Although stainless steel appliances are often not considered aesthetic, many practitioners choose stainless steel appliances because they are relatively inexpensive and yet provide satisfactory control over movement of the associated teeth.
However, stainless steel is an opaque material that blocks passage of light to underlying areas of the appliance base. As a consequence, portions of photopolymerizable adhesive beneath the base may not harden, especially in areas near the center of the base. Often, the practitioner may direct light toward the adhesive along two or more edges of the base of metal appliances or attempt to direct light through the patient""s tooth enamel. However, such a practice may not harden all of the adhesive beneath the base to a degree necessary to preclude unintentional debonding of the appliance when the appliance is subjected to a relatively large force.
U.S. Pat. No. 5,711,665, assigned to the assignee of the present invention, describes a method and apparatus for bonding orthodontic appliances to teeth. The appliance includes a base with an opening, and a body with a passage aligned with the opening. The passage in the appliance permits light to reach adhesive beneath a central portion of the appliance base that would otherwise remain substantially uncured. As a result, bond strength between the appliance and the tooth is increased and the likelihood of unintentional, spontaneous debonding of the appliance during the course of treatment is significantly reduced.
While the inventions described in U.S. Pat. No. 5,711,665 constitute a significant advance in the art, there is a continuing need to improve the construction of orthodontic appliances and methods of orthodontic treatment. Preferably, such improvements can be adopted with relatively little additional expense, and yet significantly enhance the state of the art such that the practitioner and the patient can both benefit from the improvements.
The present invention is directed to an orthodontic appliance that has a base and at least one passageway extending through the base. An element is received in the passageway and is made of a material that transmits actinic radiation. The element functions as a xe2x80x9cwindowxe2x80x9d to enable light to reach underlying regions of the appliance base so that hardening of the adhesive is facilitated. The window also hinders movement of the adhesive through the passageway as the appliance is placed on the tooth surface, such that the necessity of clean-up of adhesive near the front side of the passageway is avoided.
Optionally, the element is made of a material that slowly releases fluoride in order to inhibit the formation of caries in the vicinity of the appliance. As another option, the element is made of a material that transmits actinic radiation, but also is tinted to provide a certain color when viewed by the practitioner. The color may be selected from a set of colors that are part of a color-coding system to identify certain types of appliances, or to identify the type or location of the tooth on which the appliance is to be mounted.
As an additional option, the element may include one or more optical fibers to facilitate transmission of light to the adhesive. As an example, a number of optical fibers may be embedded within a portion of the element that is received in the passageway, and the fibers may extend radially outwardly toward a periphery of the appliance base. When actinic radiation is directed toward the element, a portion of the light passes through the fibers and to regions of the adhesive that are remote from the passageway.
In more detail, the present invention in one aspect concerns an orthodontic appliance for attachment to a tooth. The appliance includes a base having an outer surface and a body extending from the base in a direction away from the outer surface. The orthodontic appliance also includes a slot next to the body for receiving an archwire, and a passageway extending through the base. The orthodontic appliance additionally includes an element that extends in the passageway. The element is made of a material that transmits actinic radiation.
Another aspect of the invention is directed toward a method of bonding an orthodontic appliance to a tooth. The method includes the act of providing an orthodontic appliance having a passageway that extends toward a base of the appliance and an element extending in the passageway. The method also includes the acts of placing a quantity of photocurable adhesive on the base of the appliance, and placing the appliance on the tooth. The method further includes the act of directing actinic radiation through the passageway and the element in order to facilitate curing of the adhesive.
An additional aspect of the invention is directed toward an orthodontic assembly. The assembly includes an orthodontic appliance having a base with an outer surface. The assembly also includes an orthodontic adhesive that extends along at least a portion of the outer surface. The assembly further includes at least one optical fiber that is received in the adhesive and extends along the base.
The present invention is also directed toward a method of bonding an orthodontic appliance to a tooth. This method includes the acts of providing an orthodontic appliance having a base with an outer surface, and placing a quantity of light-curable adhesive on the outer surface. The method also includes the acts of placing at least one optical fiber in the adhesive, and positioning the appliance on the tooth. The method further includes the act of directing a source of actinic radiation toward the at least one optical fiber in order to enhance distribution of the actinic radiation in the adhesive.
The present invention is further directed toward a method of making an orthodontic appliance. This method includes the acts of providing a ring having a channel extending along an inner peripheral surface, and making a series of passageways through the ring in generally radial directions, wherein at least some of the passageways extend into the channel. The method also includes the acts of directing a polymeric material into the channel and into at least some of the passageways, and hardening the polymeric material. The method further includes the act of shaping a number of appliance from each ring, wherein each appliance includes a portion of the channel, at least one passageway and a portion of the hardened polymeric material.
Other aspects of the invention are described in more detail below and are illustrated in the accompanying drawings.